1. Field of the Invention
The present invention relates to a process for the preparation of a synthetic mordenite molded body, in which a molded body of a starting mixture is first prepared and the molded body is calcined and then crystallized.
2. Description of the Related Art
Mordenite zeolite is a kind of a naturally produced zeolite, and various processes for synthesizing this zeolite have been proposed. Most of these proposals are directed to the production of mordenite crystal powders.
When synthetic mordenite is industrially utilized, use of a mordenite crystal powder is often difficult and it is ordinarily used after it has been molded into spheres, extrudates or other appropriate shapes.
However, since a zeolite crystal powder has no self-bondability, when a molded body is prepared, in order to impart appropriate plasticity and strength, an organic or inorganic binder is ordinarily used. As the inorganic binder, there can be mentioned clay minerals such as kaolin and montmorillonite, and silica sol and alumina sol. However, often the mechanical strength of the thus prepared mordenite molded body is drastically reduced by a severe treatment such as an acid treatment or heat treatment in the process of forming a catalyst. Furthermore, even if the mechanical strength is maintained at a certain level, the zeolite component is diluted by the added binder, and in order to impart a mechanical strength sufficient to resist industrial application, the amount of the binder should be increased. Moreover, if a molded body of this type is used, sometimes a calcination product of the binder, such as a clay mineral, causes an undesired side reaction.
Several processes have been proposed in which a molded body of a starting mixture is formed instead of a molded body composed of a mixture of a mordenite powder and binders, and the molded body is calcined and crystallized to obtain a synthetic mordenite molded body having substantially the same shape as the shape before the crystallization.
In these conventional processes, however, no special contrivance is made in the step of calcining the molded body, or the step of withdrawing the synthetic mordenite molded body from a reaction vessel or washing this molded body after crystallization. The calcination temperature and time for the molded body are only mentioned in Japanese Examined Patent Publication Nos. 40-18614 and 45-38975. In the process disclosed in Japanese Patent Publication No. 40-18614, a large amount of powdery mordenite is formed as a by-product, in addition to a synthetic mordenite molded body, and this powder adheres tightly to particles of the molded body. Accordingly, the particles of the molded body agglomerate to form a large mass, and withdrawal from the reaction vessel and washing become difficult.